The present invention relates to fastener systems of the blind or one side access type, for use in mechanically connecting a threaded member to a sheet of material, and for an electrical connection.
Fastener systems are used to enable various screw threaded members, either male or female, to be secured to workpieces, which workpieces are in the form of flat sheets or the like. Typically, a fastener system is disposed in a hole or aperture provided in a sheet of metal or the like, to which a threaded member is to be attached. Thus, the fastener system has internal threading where a bolt is to be received, or may be in the form of an externally threaded member, where a nut is to be received. Whether the system has male or female threads, an important requirement is that it not torque loose upon being subjected to a twisting applied load, as in tightening a bolt or a nut. The system should be able to sustain a relatively high twisting or torquing load, imposed by a mating bolt or an associated nut, without rotating relative to the workpiece. At that load at which rotation occurs, the system is said to torque out. It is desirable, therefore, that a fastener system have a high torque-out value, which desideratum has not been previously obtained where a satisfactorily light-weight fastener system has been used in connection, particularly, with very thin sheets or workpieces, which are in some instances of relatively soft material. The problem is greatest in connection with the attachment of members through the use of fastener systems to thin aluminum sheets of relatively low hardness value, such as are used in many aircraft and aerospace applications.
Another requirement for such fastener systems is that it be held securely to the workpiece against axial movement, so that it will not come out of the hole in the workpiece upon application of an axial load.
As above mentioned, such fastener systems are particularly useful in blind hole applications, which frequently occur in the aircraft and aerospace field, and it is in this field, in particular, where weight considerations are of such great importance. Hence, it is another desideratum that such fasteners be applicable from one side of the workpiece only, and also that they not extend for a very great distance beyond the back surface of the workpiece, as in many situations, the space available for a fastener to be inserted, on the blind side of the workpiece, is very limited.
There have been provided in the prior art a number of suggestions for blind fastener inserts. These have included inserts which provided a sleeve member having a first portion of its axial length which was adapted to be expanded radially outwardly into engagement with the material in a workpiece defining a hole into which the sleeve member had been inserted, the sleeve member also having a bulbing portion which extended on the blind side of the workpiece. An expander member, having internal threads, was provided, shaped and dimensioned relative to the sleeve member so that upon axial movement thereof relative to the sleeve member, it caused the sleeve member to expand radially outwardly, the expander member also including a head which served to bulbously deform a bulbing portion of the sleeve member when the expander member was moved axially relative thereto. The provision of such blind fastener inserts has found acceptability by the purchasers thereof, such as aircraft and aerospace manufacturers, but their performance has not been as great as is desired, in connection with the above mentioned factors of torque-out of the insert relative to the workpiece, axial pull out of the insert from the workpiece, and in addition, there is the problem that the threaded member could rotate relative to the sleeve, after the fastener insert is in place, and a torque is applied to the threaded member.
Accordingly, it is the general object of the present invention to provide a blind fastener system of the above discussed type, having improved performance characteristics, as above discussed, while also being of relatively light weight, and not requiring a large space on the blind side of the workpiece.